Largest man-made harbour in the world, 1842
The piers
John Rennie designed the twin piers after an Act of Parliament in 1817. The East Pier's first stone was laid by the Lord Lieutenant, Earl Whitworth, that same year. The granite came from a purpose-built quarry in Dalkey, carried on tramlines specifically laid for the project. By 1842 both piers were complete, with a lighthouse on the East Pier and a gun saluting station - one of only a few ever built in Ireland. At that moment, Dún Laoghaire had the largest artificial harbour in the world.
Sandycove, 2 km north. Free entry.
The Joyce Tower
The Martello tower at Sandycove Point was built by the British in the early 19th century against the threat of Napoleonic invasion. In September 1904, James Joyce stayed there for six days as a guest of his university friend Oliver St John Gogarty, who had leased it from the War Office with a plan to 'Hellenise' Ireland. The stay ended after a midnight incident involving a loaded revolver. Joyce left; the tower stayed. His novel Ulysses opens on its roof, and the museum that has been there since 1962 holds his letters, his walking stick, and various other possessions. Admission is free. It is a short walk north from the town along the seafront.
Busiest public library in Ireland
The Lexicon
The dlr LexIcon opened on the waterfront in December 2014 - a five-storey building that won multiple awards on opening. It is now the busiest public library in Ireland by visitor numbers: four million people since it opened, more per year than most Dublin attractions that charge admission. The building sits directly opposite the National Maritime Museum in the old Mariners' Church. On a Sunday morning, between the market outside and the reading rooms inside, it is the best argument for public infrastructure you will find in this part of the city.
In the old Mariners' Church, Haigh Terrace
The National Maritime Museum
The National Maritime Museum of Ireland opened in 1978 inside the former Mariners' Church on Haigh Terrace - a 180-year-old building that has found a second purpose as good as its first. The collection covers Irish maritime history with maps, models, navigation equipment, and the stories of ships and the people who crewed them. Access is either from Georges Street Upper or from the seafront side via steps beside the Lexicon.